Have an option where players can choose whether or not they want a sort of pause/cut screen to occur when talking to an NPC. Some players (such as myself) get impatient and do not like to have to wait when trying to buy items, accept quests, etc. so the small pause that occurs when we have to talk to an NPC gets us annoyed at the game.
Make the EXP and HP/Mana bars bigger as well as have numbers on them. I think it'd be more helpful if there were actually numbers so that the players themselves can be able to tell which HP/Mana potion they should use while fighting instead of using a HP potion that will heal them too much or too little. Having the EXP bar with numbers would make it less annoying than having to hover the cursor over it whenever wanting to check how much more EXP is needed for the next level.
Also, I personally think that it would be nice if monsters can not attack you when you're "praying" and trying to accept or complete a quest. I have died numerous times from monsters while praying even though I was sure that I was done running away from monsters or was not near any aggro monsters.
These were just the minor annoyances that I hope can get corrected before the OBT begins. I only played the CBT for a couple of days so I'm not sure what else to suggest. Overall though, I think it's a nice game. I'm glad that I went to the WarpPortal panel and lounge at the AM^2 convention the past weekend where the WarpPortal staff gave me a CBT code.
